Skip level one, which is small and tedious. Skip to level two, which is excellent; it's a simple slaughter-like techbase, but there are hundreds of monsters and it's a great fun big fight on UV. Level three is dull and anonymous (you can't rationally pistol-start it, and it's just a lot of platform jumping) but level four is a fantastic castle towering out of a lava sea. It also has platforms, but fewer. Levels three and four are basically two halves of one big level. This is excellent.